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Resveratrol: The New Weight-Loss Supplement?

Experts say that taking resveratrol, an antioxidant in red wine, grapes, and berries, may help boost endurance, prevent weight gain, and improve energy. Are the claims too good to swallow? FITNESS investigates.

Antioxidants in Pill-Form

Stepping, Spinning, Pilates, dance: Rebecca Visconti, 29, is no stranger to staying fit, but soon after she started her current job, her gym time suffered. "My workday begins at 7 a.m., and I stay up longer than I should to see my husband, who comes home late from his job," says Rebecca, an analyst for an Internet technology company in Dallas. "I needed more energy to get back to working out." One day while browsing the Web, she stumbled upon an online news segment about resveratrol. This antioxidant compound, found naturally in wine, grapes, blueberries, cranberries, and peanuts, was now available in a supplement form, said the report, and could boost energy, maintain body weight, and increase muscle endurance.

Intrigued, Rebecca did some more research and eventually ordered a bottle of resveratrol. Once it arrived, she eagerly popped the pill, and one the next day and the next. Within a week of her starting her new morning ritual, her energy improved. "It feels like a caffeine rush," she says. "I'm more alert and awake." Her motivation has skyrocketed too. "I used to be dedicated to my workouts for a week or two, then start to slack off. Since I began taking resveratrol, my drive to exercise has remained much higher." She's also been able to increase the intensity of her workouts without feeling tired.

"I'm definitely in better shape than I was before taking resveratrol," she says. "I have greater muscle tone and endurance." Of course, Rebecca isn't sure whether to credit her power surge to the supplement, the conditioning from her tougher workouts, or the placebo effect. "What I do know is that without this boost in energy, I couldn't handle my new exercise routine," she says.

A Budding Trend

Rebecca is part of a fast-growing group of women who have turned to resveratrol to enhance their already healthy lifestyles. Sales of the recently popularized supplement are estimated to be upwards of $30 million annually, according to the Nutrition Business Journal. Resveratrol is now one of the top five best-selling supplements available at the Vitamin Shoppe, a national chain of health and wellness stores, with purchases having more than doubled between 2008 and 2009. Much of the initial excitement about the supplement revolved around its potential to expand longevity and its promise to lower the risk of heart disease, type 2 diabetes, a variety of cancers, and age-related problems like cataracts and bone loss. Today, however, among the ongoing medical explorations, one of its most immediate possibilities lies in the realm of fitness. "Looking at the research so far, though more is needed, resveratrol has unprecedented promise for improving people's physical endurance and helping them control their weight," says James Smoliga, PhD, assistant professor of exercise physiology at Marywood University in Scranton, Pennsylvania. Resveratrol is a source of high hopes, though much about it remains unknown.

"Even though I'm leery when I hear something described as a panacea, I feel very positive about recommending resveratrol because of the research behind it," says certified trainer Rob Smith, founder of the Body Project, a Minneapolis-area personal-training studio.

Yes, there is a plethora of research, but most of it is on animals. What these studies have shown, however, is encouraging: Resveratrol appears to activate enzymes that help muscles use oxygen more efficiently, a performance enhancement known to runners as higher VO2 max. (In simplified terms, the higher your VO2 max, the lengthier and more intense the workout you can handle.) "When you process energy more efficiently, you increase endurance," Smoliga says. "I take it myself and definitely have more stamina because of it," says Smith, who estimates that 40 of his clients also take the pill. "I can see that they're able to push themselves further than before."

Resveratrol's Get-Fit Promise

Fitness experts started to take notice of resveratrol in 2006, when the journal Cell reported that mice given the antioxidant ran nearly twice as far on a treadmill as unsupplemented critters. The treatment "significantly increases the animal's resistance to muscle fatigue," researchers concluded. Translation: More energy and less muscle exhaustion led to a better workout. "It's as if you could put the benefits of a healthy diet and exercise in a pill," Smoliga says.

The hypothesis? Resveratrol stimulates enzymes called sirtuins, which control important functions throughout the body, including DNA repair, cell life, aging, and fat production. "Sirtuins may also increase mitochondria, the powerhouses inside cells where nutrients and oxygen combine to make energy," says Felipe Sierra, PhD, director of the division of aging biology at the National Institute on Aging at the National Institutes of Health. Sure enough, mice on resveratrol had bigger, denser mitochondria, so their charged muscles were better able to use oxygen. In theory, this means that resveratrol may be able to help you work out longer or harder or both before your muscles become too fatigued to perform. These more intense workouts will then condition muscles for even greater effort the next time you lace up, for a continuous cycle of improved fitness.

Again, research outside the laboratory has been limited: In one of the few completed human trials, 90 sedentary men and women were given a resveratrol-based cocktail or placebo daily for 12 weeks. After three months, everyone jumped on treadmills. "While they all hit the same levels of intensity, the resveratrol group exerted less effort while exercising," says Smoliga, who led the study. What's more, they also had significantly lower heart rates during exercise — the equivalent of the results of three months' light to moderate training — apparently just from taking the daily supplement.

Hillary Hallows, a 33-year-old sales and marketing executive in Phoenix, can relate. She started using resveratrol about four months ago after hearing about it from a client. "My friend was getting great results, and I trusted her. Plus, I wanted to get more out of my workouts and have extra energy," she says. As with the human trial results, Hillary found that she could push herself further with less effort. "I hike at least three times a week and walk my dogs twice a day, and have found that I'm much less tired afterward," she says. "I have a long day — I'm up at 5 a.m. and in bed at 11 p.m. — and I used to feel pretty wiped after a hike or at the end of the day." Not anymore. A plausible explanation: Her resveratrol-primed muscles are using oxygen more efficiently than they used to.

Resveratrol and Weight Loss

For all the evidence, anecdotal and otherwise, about resveratrol's exercise benefits, manufacturers' claims that the supplement helps people lose or maintain weight are harder to substantiate. "From what I see on myresveratrolexperience.com, one of the primary reasons women in their 20s and 30s are taking it is that they think it'll help with weight loss," says Mark Swartz, who created the blog about two years ago to chronicle his and other people's experience with the supplement. Some proponents say it works in part by interacting with blood sugar. "Studies show that resveratrol boosts our muscles' ability to absorb glucose from food. This means that more calories go into muscles and fewer go into fat cells," Smoliga says. Indeed, research presented at a conference of the Endocrine Society showed that in the laboratory, resveratrol inhibited production of mature fat cells and hindered fat storage — at least at the cellular level. In addition, a study found that mice fed a high-fat diet with resveratrol weighed almost the same as those served a non-high-fat diet without the supplement. But because, for some, resveratrol appears to increase the ability to exercise more frequently and intensely, it's hard to pin down the real source of weight maintenance.

Moreover, the supplement's long-term safety has yet to be proved. While one human study found that ingesting a one-time dose of up to five grams had no serious ill effects, that experiment lasted only a day. (Of course, most people who try resveratrol take more than one dose.) "The studies are too short," Sierra says. "We just don't have any data on long-term effects in people."

Safety Concerns

Establishing supplement safety can take decades, and over time, in some cases, surprising dangers can be revealed. "Not long ago, vitamin E was all the rage," says Christopher Gardner, PhD, associate professor of medicine at Stanford University School of Medicine's Prevention Research Center. Vitamin E is an antioxidant thought to help protect against a range of diseases, like the hopes for resveratrol. But a 2005 report found that high doses of E could actually increase the risk of death. "It took 30 years to show that vitamin E supplements may have had negative effects in the large amounts that were often recommended," Gardner notes.

What is proved to be safe and healthy: consuming moderate amounts of natural sources of resveratrol. "Because of the unknowns, I'd rather people enjoy a glass of wine now and then instead of taking supplements," Gardner says. And research suggests that moderate amounts of wine can lower the risk of cardiovascular problems. Red wine has the highest concentration of resveratrol, with as much as 15 milligrams per bottle in types like pinot noir, depending on grapes, vineyard conditions, and other factors, but the content even in wine ranges widely; grape juice has about a half milligram per liter; and cranberries, blueberries, and peanuts contain trace amounts.

With no true consensus on the ideal amount of resveratrol necessary for measurable fitness perks, many experts advise women to proceed with caution. "Do you really want to experiment on yourself?" asks Sierra, who advocates getting in shape sans supplements. That opinion is shared by many FITNESS advisory board members we surveyed, including Jade Alexis, certified personal trainer and Reebok Global Instructor. "I typically frown on these seemingly quick, easy fixes," Alexis says. "I believe that eating right, exercising regularly, and getting sufficient sleep will keep us healthy."

Still, Rebecca, Hillary, and countless others are willing to take their chances. "I haven't experienced any downsides to resveratrol," Hillary says. "And I don't expect to, or I wouldn't be taking it and risking my body or my health."

"It's good to be cautious," adds Rebecca, who takes just 125 milligrams a day to hedge her bets. "I'm sensitive to drugs and supplements and have tried herbal products that have caused side effects, like making me dizzy. That's why I'm taking only a small dose of resveratrol. Even so, I think it may be helping me get the results I was looking for."

What to Know Before You Take It

Here's what to think about before popping a resveratrol pill.

Take an Rx inventory. Studies suggest that the supplement could increase the risk of bleeding if you're taking blood thinners, anticoagulants, or nonsteroidal anti-inflammatory drugs. Resveratrol may also interfere with the body's ability to metabolize various meds, including statins, calcium channel blockers, and immunosuppressants, potentially causing a toxic buildup of medication. Talk to your doc before taking any supplement.

Check the label. Look for products that contain trans-resveratrol, which is found in nature. Beware of words like complex, formula, and blend, which indicate a mix of ingredients that may include only small amounts of resveratrol.

Buy tested brands. Biotivia, Longevinex, and Swanson have passed purity and ingredient tests performed by ConsumerLab.com, an independent company that checks supplements.

Three Performance Boosters

Resveratrol isn't the only game in town. Here, Mark Moyad, MD, MPH, director of preventive and alternative medicine at the University of Michigan Medical Center and FITNESS advisory board member, gives the scoop on more fitness enhancers.